1. Field of the Invention
The present invention relates to a thermostat device controlled by a valve element having a valve shaft, especially to a bottom bypass structure of the thermostat device which has a bypass channel provided in the lower reaches side of the valve element disposed in a circulation channel of fluid, allowing the fluid to bypass to the lower reaches side of the circulation channel in accordance with an opening and closing situation of the valve element, and a switch valve to open and close the bypass channel.
2. Description of the Related Art
Generally, a thermostat device disposed in a cooling system for an engine and the like, has a sensor case embedding a heat expansion element which expands and shrinks when sensing the temperature change of coolant filled in a circulation channel of the cooling system, and has the function of maintaining the coolant at a predetermined temperature through opening and closing of the valve caused by volume changes through expansion and shrinkage of the heat expansion element.
A poppet type thermostat device having a bypass valve as shown in FIGS. 10 and 11 is an example of a commonly used thermostat device. This thermostat device 1A is a thermostat which has a first valve element 6' and a second valve element 23 (bypass valve). While the coolant in the circulation channel 4 is blocked by closing the first valve element 6' when the coolant is at a low temperature during warming up of an engine E or the like (refer to FIG. 10, the coolant is circulated toward an inlet side of the engine E through a bypass channel 3 from an outlet side of the engine E by opening the second valve element 23 (bypass valve).
When the coolant is warmed up to temperatures exceeding a predetermined temperature, a heat expansion element of a sensor case 21' opens the first valve element 6' through a piston rod 22' so that the circulation channel 4 of the coolant is opened and the heat expansion element closes the second valve element 23 (bypass valve) to block the bypass channel 3.
The thermostat device 1A having the above functions can be disposed at an inlet side or an outlet side of an engine in the cooling channel 4, but it is not used only for cooling an engine in high temperatures and the like. And when considered environmental matters such as an emission or fuel efficiency, and relation to other parts having another temperature sensing function, from a standpoint of maintaining an accurate water temperature of the coolant and correspondence to a rapid change of the water temperature, it is more popular to be disposed at the inlet side shown in FIGS. 5.
When the thermostat device 1A is disposed at the inlet side of an engine and the like, that is, at a place where the coolant coming from the engine E through the bypass channel 3 and the coolant coming from a radiator R are mixed, as compared with the effect in the case of disposing at the outlet side, it has the effect that the range of the water temperature hunting becomes smaller because of mixing of the coolants, and a pressure difference fluctuation becomes small due to the balance between the bypass channel 3 and the radiator R.
When the thermostat device 1A reaches a predetermined lift, since the second valve element 23 (bypass valve) blocks the bypass channel 3 and causes all the coolant to flow to the radiator R, it becomes possible to improve the radiation characteristic of the radiator R, which results in an advantage for the temperature control of an air conditioner.
In the above described conventional poppet type thermostat device 1A, since the first valve element 6' and the second valve element 23 (bypass valve) are disposed in the circulation channel 4, and a piston rod 22' to drive these valve elements 6', 23 (bypass valve) is always kept in the coolant, according to circumstances, the coolant penetrates into the piston rod 22' and the piston guide 19, which has an adverse influence on the sliding function.
Some ingredients in the coolant may sometimes corrode the structural members and impair the functions. If this happens, a smooth passage of the coolant through the circulation channel 4 or the bypass channel 3 can not be expected and moreover it may have a serious effect on the driving of the engine E.
Besides, since the sensor case 21' which serves as a sensing portion of the coolant, the first valve element 6' which is a sliding portion, and the second valve element 23 (bypass valve) are disposed in the circulation channel 4, the flow resistance of the coolant is enlarged. Therefore in order to obtain a predetermined flow amount, an increase of the valve diameter of the first valve element 6' is required, which disturbs a size reduction of the thermostat device 1A itself.
Further, the coolant flows into the thermostat device 1A from different directions of the circulation channel 4 and the bypass channel 3, and the sensor case 21' which serves as a sensing portion is not hit by the coolant which is a mixture of the coolant flowing in from both direction. Consequently, the temperature of the coolant can not be accurately sensed in some circumstances.
In a thermostat device which has the function of forcibly opening the valve element 6 by heat-expansion of wax in a sensor case using a heating device, when trouble such as leakage of the coolant or breaking of shield wire happens, it results in a disadvantage in handling control due to the difficulty in replacement.
As a substitute for the above described poppet type thermostat device 1A, there is a thermostat device 1B having a mechanism which has a valve element to block the circulation channel 4 and a detecting portion to detect the temperature of a fluid in the circulation channel 4 and has a mechanism in which a driving mechanism to drive the valve element around the valve shaft is disposed outside the circulation channel 4 as shown in FIG. 13 (refer to Japanese Utility Model Laid-open No. Hei 2-145623).
In the thermostat device 1B, it may be possible to protect functional components from coolant or to control the flow amount to some extent in accordance with a required flow amount by increasing the valve diameter, however, from the structure of the valve element 6', that is, since the valve element to control the flow amount is only one, it is difficult to accurately control the flow amount of the bypass channel 3 and the flow amount of the circulation channel 4.
Therefore, similar to the poppet type thermostat device 1A explained hereinbefore, functions such as a reduction of the pressure difference fluctuation by taking the balance between the bypass channel 3 and the radiator R, and prevention of the water temperature hunting, can not be fully effected.
A bottom bypass structure of the thermostat device relating to the present invention is developed in consideration of these disadvantages and the object of the invention is to provide the following bottom bypass structure of a thermostat device.
In the thermostat device having a valve element with a valve shaft, a bottom bypass structure of a thermostat device which can materialize a stable action of the valve element, prevent from over shooting and hunting, and can reduce in size of the thermostat device itself.